Screw thread cold-rolling machine



June 19, 1962 R. KOHLER 3,039,334

SCREW THREAD COLD-ROLLING MACHINE Filed June 13, 1960 3 Sheets-Sheet 1 June 1962 R. KOHLER 3,039,334

SCREW THREAD COLD-ROLLING MACHINE Filed June 13, 1960 3 Sheets-Sheet 2 D01 van Iv r.-

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June 19, 1962 R. KOHLER 3,039,334

SCREW THREAD COLD-ROLLING MACHINE Filed June 13, 1960 3 Sheets-Sheet 3 8 3 g! gay y 3n vuvl'or flan! PM,

A-l-hs rnaf United States The invention rel-ates to the cold rolling of screw threads by the method consisting in rolling the blank between two forming wheels having parallel axes and rotating in the same direction, each of said wheels being of hard metal and having an outer screw threading which is adapted to be impressed onto the blank by a radial upsetting of the metal and form the screw threading in the blank without removal of metal.

The known machines of this type comprise a positive feed device which is exactly synchronized and in phase with the rotational speed of the forming wheels; these machines have the following disadvantages: low output owing to the reciprocating motion of the feed device or to the inertia of the forming wheels which, in the course of operation, execute substantial movements of translation or angular displacements about their axes and, after the screw threading of each blank, resume their initial position; complicated, costly and fragile synchronizing devices; expensive tooling having limited working life; delicate in operation.

The object of the invention is to eliminate these disadvantages and to provide a simple machine which is economical in operation, has a high output, is reliable and regular in operation and has a low tool consumption.

A particular object is to provide such an arrangement of the various component parts that the machine lends itself to a simple, continuous, and perfectly aperiodic and asynchronous feed system.

The machine according to the invention comprises two screw threaded forming wheels mounted on parallel spindles and rotating in the same direction at different tangential speeds, and means for feeding the blanks to be rolled in the working region between the two wheels by mere gravitational force or under the effect of a non-positive continuous force of the same order of magnitude as their weight, without regard to periodicity or synchronisrn with the rotation of the wheels.

Applicant has discovered that it is possible to roll the blanks and obtain screw threading of sufiicient quality without need to provide the machine with a positive feed device operating with a well-determined periodicity in synchronism and phase with the rotation of the wheels and that the feed can be considerably higher than in synchronous feed machines.

Applicant has furthermore discovered that, notwithstanding these advantages of simplicity and high output, the screws obtained have remarkable precision, finish and quality if at least one of the forming wheels is so mounted as to undergo oscillation on its spindle.

One of the features of the invention therefore resides in the fact'that at least one of the wheels is so mounted on its spindle as to undergo, relative to a plane perpendicular to the latter, slight movements of angular oscillation and is associated with elastically yieldable return means biasing it to a mean position. When only one of the forming wheels is mounted to oscillate, the maximum oscillation corresponds to one pitch of the screw threading to be rolled which, bearing in mind the diameter of the wheels (for example 200 mm.) represents a very small angle of oscillation. When both wheels are oscillatory, this oscillation is reduced by half. It is not necessary that the wheels return to their mean position before the following blank is introduced into the working region, and this is 7 why the machine has a considerably high output.

atet "ice Further features and advantages of the invention will be apparent from the ensuing description of the principle of the invention and of a preferred embodiment of the latter with reference to the accompanying drawings, to which the invention is in no way limited.

In the drawings:

FIG. 1 is a diagrammatic plan view of the forming wheels showing the principle of the invention;

FIG. 2 is a corresponding side view thereof;

FIGS. 3 and 4 are explanatory diagrams;

FIG. 5 is a side view of the feed device;

FIG. 6 is a corresponding plan view, and

FIGS. 7 and 8 are axial sectional views of two modifications in the mounting of the forming wheels on their spindle.

With reference to FIG. 1, two forming wheels A and B, outwardly screw threaded in accordance with the screw threading to be formed on the blanks, rotate about their parallel spindles having axes O and O in the same direction and at different tangential speeds V and v, the tangential speed V of the wheel A being higher than that v of the wheel B so as to produce a translation of the blanks R, R R etc. during the thread rolling operation.

The difference between the tangential speeds can be obtained in three ways:

(1) The wheels A and B have the same diameter and the same number of threads but rotate at different angular speeds.

(2) The wheels A and B have diiferent diameters and respectively diiferent numbers of threads and rotate at the same angular speed.

(3) The wheels have different diameters and respectively different numbers of threads and rotate respectively at different angular speeds.

The spindle of one of the wheels is movable in the plane XY so as to permit regulation of the centre distance 0, O in accordance with the screw threading to obtain.

A continuous feed device which is completely asynchronous and aperiodic relative to the motion of the forming wheels feeds the blank R, R R etc. in succes- ,sion between the wheels, the longitudinal axes of these blanks being parallel with the spindles of the wheels as they approach the working region.

To produce a correct screw threading on the blank, the screw threads on the forming wheels must always be in a certain correlation at a given instant, corresponding to an instantaneous position of the blank relative to the two forming wheels, that is to say, the screw threads impressed in the blank by the two wheels must be situated on the same helix. To facilitate the description, this correlation will be hereinafter designated by the expression the wheels are in phase. FIG. 2. shows that when a blank R at the end of the screw threading op eration is situated on the middle line XY intersecting the centres O and O of the wheels, the homologous lines of contact of the wheel A and the wheel B with the blank R are axially oifset by a distance corresponding to half the pitch of the helix, each thread crest of the wheel A being located opposite the thread bottom of the wheel B and vice versa. Before the screw threading operation is completed, that is, in the positions of the blank outside the plane XY, the correlation of the screw threads of the two wheels no longer corresponds to an angular spacing of on the blank. Thus, the points of contact of the blank R with the wheels are no longer axially offset by a half-pitch. It is, however, obvious that a certain correlation must exist between the thread crests and bottoms at each instant on the two wheels to obtain a correct screw threading of the blank. This is the correlation designated hereinbefore by the expression in phase and which can also be expressed freedom to slightly slide along their spindle.

instating that the homologous impressions produced on the blank must be situated on the same helix.

When a blank, guided by the feed device, reaches the working region between the two wheels without a positive thrust and by the action of a weak force, of the order of its own weight, in a direction parallel with the spindles supporting the latter and in contact with the wheels, two situations are possible:

(1) Either the wheels are in phase."

In this event, which is a mere chance, the blank starts to rotate in the direction corresponding to the arrows and is driven between the wheels at a speed of translation It is screw threaded in the course of its passage between the wheels and thereafter expelled beyond the plane XY.

(2) Or the wheels are not in phase.

This is the most frequent case. Wheel A tends to drive the blank in the working region by rotating it about the axis of the blank and exerting thereon a heavy pressure. Wheel B, on the other hand, tends to urge the blank out of this region. Under the effect of the slight feeding thrust hereinbefore mentioned, added to the tangential force produced by the rotation of wheel A, the blank remains in contact with the wheels. Wheel A impresses onto the blank shallow furrows (FIG. 3) and the opposite smooth surface of the blank slides over wheel B, owing to the lighter pressure, until the two wheels come into phase. At this moment, the bottoms of the furrows coincide with the crests of the threading of wheel B (FIG. 4) and the blank is driven into the working region as mentioned. hereinbefore, screw threaded and evacuated.

Thus it is found surprisingly that the feed of the blanks can be continuous, aperiodic and completely asynchro nous with respect to the operation of the forming wheels and that the correct entry of the blanks in the working region occurs automatically.

A machine where the forrningwheels have a constant relationship to their geometrical axis of rotation is capable of producing satisfactory screw threads for a good number of current uses. However, the machine can be still improved if it is desired to produce absolutely faultless screw threads with the minimum of waste. It will be recalled that the correlation between thread crests and thread bottoms of the forming wheels must be modified progressively from the effective entry of the blank in the working region to its exit. Further, upon entry of the blanks in the working region, the contacts between the wheels and the blank occur on the outside diameters of the wheels and the outside diameter of the blank. However, when the aXis of a blank reaches the line XY (FIG. 1), the contact between the wheels and blank occurs on the pitch diameters of the wheels and the pitch diameter of the threaded blank. Therefore, with forming .wheels having geormetrical axes constantly in register with the axes of rotation, the correlation above referred to could not be preserved throughout the rolling operation.

There are several means for ensuring the desired cor- 1 relation so as to avoid defects resulting from the foregoing considerations. Thus the forming Wheels could have a certain freedom of rotation relative to their spindles, that is, they could be temporarily allowed small speed variataions dV or dv, or they could have a certain However, these solutions did not prove satisfactory, both as regards the quality of the screw thread obtained and the output of the machine, which is seriously effected by the inertia of the forming wheels in rotation or translation;

a plane perpendicular to said spindles, and to interpose between the wheels and their spindle an elastically yieldable biasing means returning the wheels to a position perpendicular to said spindles when the wheels are relieved from stress. 7

Experience has shown that, With a quite simple construction, perfect operation and considerable output are obtained.

It is easy to calculate the output of a machine based on the foregoing principles. I

Let and f be the numbers of threads of the forming wheels A and B respectively;

W and W the angular speeds of the wheels A and B imparting thereto the tangential speeds V and v respectively.

Let it be supposed that the forming wheels are in phase at instant to (there being correlation between the threading of the two wheels at the points of contact of the latter with the blank), at the moment the blank comes in contact with the wheels. The respective numbers of threads and of the two Wheels passing through these points of contact in a given interval of time are different. Correlation will be ensured for the first time only at instant t after a time t, so that:

(fA AfB B) whence:

Correlation will occur at time intervals t which are equal to this value. The frequency of reproduction of the correlation is equal to 1, namely f W -f W This value also represents the theoretical output of the machine.

This theoretical output is a maximum and cannot be attained for parts such as for example screws having a head or projection whose diameter is larger than that of the threading. In this case, it will beunderstood that a blank can only enter the working region every other 2 or n times the two wheels are in phase, according to the diameter of the head or projection. In this case, of course, the output of the machine is divided by 2 or n.

It has been ascertained experimentally that the output of the machine easily reaches 1500 screws per minute or more in the case of headed screws.

As an example, FIG. 5 shows a sectional view and FIG. 6 a plan view of a machine for thread rolling headed screws. The feed device comprises a slideway terminating in the vicinity of the working zone in two parallel rails 9 which are inclined at about 30 relative to the horizontal and receive the screw blanks R R R R which are suspended by their heads and tend by mere gravity to descend and automatically enter successively in contact with the wheels A and B. Wheels A and B are connected to their respective spindles 4 and 3 by an elastically yieldable device to be described hereinafter. The spindles 3 and 4 are parallel and inclined relative to the vertical at an angle of about 30. The centre distance between the spindles, the threading of the wheels and the diameter of the blanks are adjusted or designed in accordance with the screw threading to be obtained on the blanks. The spindles are driven in rotation by any driving means.

At the entrance of the working region, the head of the blanks is pressed against the upper part of the rails 9 by a spring blade to so that each blank is brought in contact with the wheels in a direction parallel with the axes of the spindles 3 and 4. The correctly screw-threaded screws fall in the direction of arrow T at the exit of the working region and are received for cleaning or packing.

When a blank is for any reason badly screw-threaded, experience has shown that its rotation about its axis is accompanied by an axial translation, so that these very few blanks are automatically rejected upwardly and can be received in a slideway 35 whence they can be recovered separately. Thus the separation of the waste is automatic.

The assembly is completed by brushes 11 which constantly clean the wheels by merely rubbing thereagainst and by nozzles (not shown) which project onto the wheel-s jets of oil for lubricating and cooling in the known manner.

Two examples of the mounting of the forming wheels on their spindles are shown in FIGS. 7 and 8. Each figure shows only one wheel; moreover in certain cases, the machine can be equipped with only one oscillatably mounted wheel, the other being rigidly mounted on its spindle.

The wheel A or B (FIG. 7) has mounted on both faces two *half-balls 40 and 41 which are centered on the Wheel and driven thereby through the medium of pins or studs 42. These half-balls are engaged in half-sockets 43 and 44. The socket 43 is held in a recess in a flange 5 of the wheel carrying spindle 3 by screws 45, and the socket 44 is held in a recess in -a nut 46 by screws 47. The wheel is driven by pins 39. Clearance i j i i are provided in the regions indicated in FIG. 7 to permit the ball 40-41, rigid with the wheel, to oscillate slightly within the socket 4344, which is rigid with the spindle 3. Rubber washers 47 and 48, interposed between the wheel and the elements rigid with the spindle, are adapted to elastically return or bias the wheel to its mean position. A locknut 48 blocked by a screw 48 prevents the nut 46 from unscrewing.

FIG. 8 shows a modification of FIG. 7, wherein the wheel is fitted on a flanged sleeve 50 and connected thereto by screws 50*. The assembly comprising the wheel and the sleeve is driven by the spindle 3 by means of pins 57. The bore of sleeve 50 receives the outer ring 49 of a swivel roller bearing 56.

The inner ring 52 of this bearing is fitted on a sleeve 54 which is made rigid with spindle 3 by a key 55. Two nuts 51 and 53 respectively block the races 49 and 52. A cap 46 closes the assembly and is held in position by a nut 48. Suitable clearances are provided to permit the oscillation of the wheel relative to a plane perpendicular to the spindle 3. Rubber washers 47 and 48 return the wheel to a position parallel with a plane perpendicular to the spindle 3.

It will be understood that other devices could be designed to provide for a slight angular oscillation of the wheels.

The invention permits to reducing the cost of the rolling operation, while providing an excellent screw thread finish. The tooling cost is itself reduced, owing to the fact that it is possible to sharpen or remachine the wheels several times, correct operation of the machine being unrelated to the precision of the diameter of the wheels.

The machine according to the invention can be used for providing screw threads having any thread profile, on any elements in the form of a body of revolution with or without a head such as, for example, metal screws, wood screws, self-tapping screws, coach screws, worms, the screw threading being of the single or multiple-start type.

Although a specific embodiment of the invention has been described, many modifications and changes may be made therein without departing from the scope of the invention as defined in the appended claims.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A machine for cold rolling screw-threading on blanks and comprising two screw threaded forming wheels mounted on two parallel spindles, said wheels being spaced apart to provide a screw thread rolling region between the peripheries of the Wheels, means for rotating the wheels in the same direction at substantially different tangential speeds, at least one of the wheels being so mounted on its spindle as to be able of undergoing slight movement of angular oscillation relative to a plane perpendicular to said spindle, and elastically yieldable return means between said last-mentioned wheel and said rotating means for returning said wheel to its mean position.

2. A machine as claimed in claim 1, wherein said rotating means comprise a ball and socket connection interposed between said last mentioned wheel and its spindle, whereby said wheel is oscillatable about the centre of said ball, said return means comprising elastically yieldable washers interposed between said last-mentioned wheel and said rotating means.

3. A machine for cold rolling screw-threading on blanks and comprising two screw threaded forming wheels mounted on two parallel spindles, said Wheels being spaced apart to provide a screw thread rolling region between the peripheries of the wheels, means for rotating the wheels in the same direction at substantially different tangential speeds, at least one of the wheels being so mounted on its spindle as to be able of undergoing slight movement of angular oscillation relative to a plane perpendicular to said spindle, elastically yieldable return means between said last-mentioned wheel and said rotating means for returning said Wheel to its mean position, an inclined slideway for yieldingly feeding said blanks into said rolling region, the spindles of said wheels being perpendicular to the inclination of said slideway in the part of the latter adjacent said rolling region, an upper guide strip adapted to engage the heads of the blanks and a spring blade in the vicinity of said rolling region for yieldably urging the heads of the blanks against the slideway and preventing overlapping of said heads.

4. A machine as claimed in claim 3, comprising, disposed at the outlet of said rolling region, on the side of the plane containing said two spindles opposite to the blank feeding slideway, a collecting slideway adapted to receive badly rolled blanks undergoing an upward translation as they pass through said region.

References Cited in the file of this patent UNITED STATES PATENTS 

